I can't remember who it's from, but there's a quote about this. Something like:
Wrestlers and other athletes are in shape, but boxers are always the fittest athletes. Why? If a runner gets tired, he loses the race. If a wrestler gets tired he gets pinned. But if a boxer gets tired, he gets the ever-loving shit beaten out of him.
Combat sports are classically one of the most "everything" sports, for which you need all forms of fitness. You must be able to explode, you must be able to sustain high output in exchanges, and you must be able to maintain a pace for round after round. And if you can't keep up in any of them then you get battered violently. Some elite boxers are able to skip either end of this spectrum -- a knockout artist might pray he never makes it to the 12th round, and a Willy Pep type fighter might rely on his footwork instead of explosive attacks -- but they need to be in aerobic shape, anaerobic-lactic shape, and anaerobic-alactic shape.
Furthermore, jogging and other long slow cardio efforts are considered by many to be the fitness base on which the other energy systems are built. That is, it's harder to develop your explosive anaerobic-alactic fitness if you're in poor aerobic shape.